Seminar 1: Concepts in Laboratory Medicine Flashcards
What is sensitivity?
The sensitivity of a laboratory test is its capacity to identify all individuals with the disease.
The formula for sensitivity:
True positives ------------------------------- x100 true-positives + false-negatives
What is specificity?
Specificity is a statistical term that indicates the effectiveness of a test to correctly identify those without the disease.
it does not refer to its ability to diagnose a “specific” disease among a group of related disorders.
One could maximize specificity by raising the threshold
This would decrease the number of false positives because everyone without disease would have a negative test result.
The formula for specificity:
true negatives
—————————- x100
true-negatives + false-positives
What is predictive value?
The population of individuals with a positive test result is the focus of positive predictive value.
The positive predictive value for a laboratory test indicates the likelihood that a positive test result identifies someone with disease.
the predictive value of a positive test is greatly influenced by the prevalence of the disease in the area where testing is performed.
The population of individuals with a negative test result is the focus of the negative predictive value.
The negative predictive value for a laboratory test indicates the likelihood that a negative test result identifies someone without disease.
What is prevalence?
The prevalence of a disease reflects the number of existing cases in a population.
What is Incidence?
Incidence refers to the number of new cases occurring within a period of time, usually 1 year.
What are false positives and false negatives?
When diagnostic threshold will misclassify some patients to create false-positives and false-negatives.
Overlap between values of people with and without the disease.
What are preanalytical variables that influence laboratory test results?
- Age
- Gender
- Body Mass
- Preparation of the patient
- Patient posture during blood collection
What are some well-known interferences in many laboratory tests?
- There are three major interferences that must be considered when selecting and interpreting the results of laboratory tests.
- These are hemolysis that makes plasma and serum red;
- elevated bilirubin that makes plasma and serum shades of orange, green, or brown;
- and lipemia that makes plasma and serum milky white.
What is involved in the analytical phase?
The second phase is the analytical phase, which is the time that the sample is being analyzed in the laboratory. Errors can occur during this process, but they are much less common now because of the high level of automation of many laboratory instruments.
- Examples of analytical errors are incorrect use of the instrumentation and the use of expired reagents.
What is involved in the pot analytical phase?
The third phase of laboratory test performance is the post-analytical phase
which begins when the result is generated and ends when the result is reported to the physician.
-Examples of errors in this phase, which are more common than analytical errors but less common than preanalytical errors, are delays in time to enter a completed result into the laboratory information system and reporting results for the wrong patient.
What is involved in the pot analytical phase?
The third phase of laboratory test performance is the post-analytical phase
which begins when the result is generated and ends when the result is reported to the physician.
-Examples of errors in this phase, which are more common than analytical errors but less common than preanalytical errors, are delays in time to enter a completed result into the laboratory information system and reporting results for the wrong patient.
How can we minimize errors in the interpretation of the laboratory results?
- it is impossible for a health care provider to understand the clinical significance of an abnormality for each test.
- in some institutions, narrative interpretations of complex clinical laboratory evaluations are prepared by experts in the field.
In most institutions, such narratives require a special request for completion, but an emerging concept is to provide narrative interpretations for all complex clinical laboratory evaluations automatically, as they are provided in radiology and in anatomic pathology.
Misinterpretation of laboratory test results has been increasingly noted as a source of poor patient outcome.
What should be done when there is no need
When there are no compelling reasons to maximize either sensitivity or specificity, the threshold value should be established to minimize the total number of false positives and false negatives.
How can we minimize errors in the interpretation of the laboratory results?
- it is impossible for a health care provider to understand the clinical significance of an abnormality for each test.
- in some institutions, narrative interpretations of complex clinical laboratory evaluations are prepared by experts in the field.
In most institutions, such narratives require a special request for completion, but an emerging concept is to provide narrative interpretations for all complex clinical laboratory evaluations automatically, as they are provided in radiology and in anatomic pathology.
Misinterpretation of laboratory test results has been increasingly noted as a source of poor patient outcome.
What is the effect of age on lab tests?
- a number of laboratory tests that have different normal ranges for patients of different ages.
- particularly important in pediatrics
- Newborns especially have many different normal ranges than adults or older children for substances in the blood and other bodily fluids.
- E.g., several of the coagulation factors do not reach adult levels for many months after birth.
As a second well-known example, the cholesterol level rises with age.
What is the effect of age on lab tests?
- a number of laboratory tests that have different normal ranges for patients of different ages.
- particularly important in pediatrics
- Newborns especially have many different normal ranges than adults or older children for substances in the blood and other bodily fluids.
- E.g., several of the coagulation factors do not reach adult levels for many months after birth.
As a second well-known example, the cholesterol level rises with age.
What is the effect of gender on lab tests?
- Different types and levels of hormones - e.g., testosterone and estradiol.
- among women, there are variations in the serum concentration of various hormones throughout the menstrual cycle.
What is the effect of gender on lab tests?
- Different types and levels of hormones - e.g., testosterone and estradiol.
- among women, there are variations in the serum concentration of various hormones throughout the menstrual cycle.
What is the effect of Body Mass on lab tests?
Muscle mass can affect the level of certain compounds, such as creatine kinase, in the blood.
Increase in serum cholesterol level with obesity - cholesterol level is related to the amount of body fat.
How do you prepare a patient for laboratory testing?
- Certain lab tests require special preparations of the patient in order to provide the most clinically useful, accurate, and precise result.
- One of the most commonly encountered patient preparations is fasting, usually for 8 to 12 hours, depending on the test.
- The serum triglyceride level can be significantly affected by eating, and fasting is absolutely required.
- Another test for which fasting is required is the fasting blood glucose used in the evaluation of a patient for diabetes.
How do you prepare a patient for laboratory testing?
- Certain lab tests require special preparations of the patient in order to provide the most clinically useful, accurate, and precise result.
- One of the most commonly encountered patient preparations is fasting, usually for 8 to 12 hours, depending on the test.
- The serum triglyceride level can be significantly affected by eating, and fasting is absolutely required.
- Another test for which fasting is required is the fasting blood glucose used in the evaluation of a patient for diabetes.
What is the correct patient posture for blood collection?
- Patient posture may affect the result for certain tests.
- There is a lower plasma volume when the patient is upright because there is a pooling of fluid in the dependent parts of the body when standing.
- When the patient is supine, there is a movement of fluid back into the circulation from the tissues. The extra volume in the circulation can dilute certain compounds in the blood.
- Best to monitor the patient in the same postural position
if the test result is affected by posture and if the values need to be compared with one another over time.
What is the difference in test results between samples of venous, arterial, and capillary blood?
- Venous blood may have a different concentration of a compound than arterial blood.
- The best examples are the blood gases that show marked differences between arterial and venous blood because of the exchange of gases in the lungs.
- There may also be a difference between capillary blood and arterial and venous blood.
- Blood glucose values may differ significantly in capillary (finger-stick) samples from venous or arterial blood.
What is the difference in test results between samples of venous, arterial, and capillary blood?
- Venous blood may have a different concentration of a compound than arterial blood.
- The best examples are the blood gases that show marked differences between arterial and venous blood because of the exchange of gases in the lungs.
- There may also be a difference between capillary blood and arterial and venous blood.
- Blood glucose values may differ significantly in capillary (finger-stick) samples from venous or arterial blood.
